1. Field of the Invention
The present invention pertains to a tool for deploying or injecting tracer materials into an earth formation through a wellbore, particularly radioactive or other highly toxic type tracer materials.
2. Background
In the development and production of hydrocarbon reservoirs, certain fluid injection processes are studied with respect to the distribution of fluid flow by mixing with the distributed fluid a tracer material which is highly radioactive. When dispersed through the reservoir the radioactivity concentration is reduced, but during the injection process the concentration in the small amount of tracer material used in the process is relatively high and the handling of this material presents several problems in regard to tools and related equipment associated with the deployment process.
In utilizing radioactive tracer materials for injection into subterranean reservoirs, usually only relatively short half-life radioactive materials at relatively low concentrations are injected in isolated areas downhole adjacent to the injection zone to be studied. Radioactive tracer materials which have relatively long half-lives or are of relatively strong concentrations and are to be injected in relatively large quantities are usually pumped with injection fluids into the wellbore from the surface. The surface injection procedure will not permit, typically, zonal isolation of the injected tracer material. However, there are many instances wherein it is desired to inject relatively high energy and long half-life type tracer materials into specific zones within a well. Moreover, known types of tools for deploying short half-life type radioactive tracer materials in wellbores have some shortcomings. Existing types of tools are not easily adapted to minimize their size for shipment from the tracer material loading source to the well site and the requirements for approved shipping containers are difficult to accommodate.
Furthermore, conventional tracer deployment tools are not well suited for loading the highly radioactive, long half-life type radioactive tracer material into the tool in the field or at the well site. The residual amounts of tracer material left in conventional tools requires that the tools be disposed of in a suitable manner and the transport and disposal process is complicated by the size of existing tools. Still further, conventional tools are not easily rinsed free of tracer material upon completion of the injection process, thus requiring that the entire tool be disposed of after only one use. The cost of known types of tools therefore makes the use of radioactive tracer materials, in many instances, prohibitive. Accordingly, there has been a need for the development of wellbore tracer material deployment tools which have advantages or features which overcome the deficiencies of prior art tools including those mentioned herein.